A smoking-gun email from Eli Manning proves he quarterbacked a conspiracy to defraud collectors by pawning off phony game-worn gear as the real deal, according to court documents obtained by The Post.

The two-time Super Bowl MVP, who has a contract with memorabilia dealer Steiner Sports, instructed a team manager to get the bogus equipment so it could be sold off as authentic, the papers say.

“2 helmets that can pass as game used. That is it. Eli,” Manning wrote to equipment manager Joe Skiba from a BlackBerry on April 27, 2010, according to the documents.

Less than 20 minutes later, Manning wrote to his marketing agent, Alan Zucker, who requested the helmets, saying: “Should be able to get them for tomorrow.”

The emails were filed Tuesday in New Jersey’s Bergen County Superior Court by three memorabilia collectors who are pressing a civil racketeering suit against the Giants, Manning, Skiba, Steiner and others, including team co-owner and CEO John Mara.

The legal filing also alleges that Big Blue failed to produce the Manning-Skiba emails — between the athlete’s old-school AOL account and an official NFL account — even though “they claim to have no document destruction policy.”

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“Since it appears that the Giants failed to preserve any emails between Manning and Joe Skiba, and the Giants are keeping Skiba on the payroll and paying his substantial legal bills, the above email exchange may be the only direct evidence that Manning knowingly gave fraudulent helmets to Steiner for sale to fans,” court papers say.

On Thursday, plaintiffs’ lawyer Brian Brook said “it appears to be the case that someone at the Giants organization deleted” those emails, as well as another, previously disclosed 2008 exchange.

In that exchange, Skiba allegedly admitted to plaintiff Eric Inselberg that Manning had asked him to create “BS” versions of a game-used helmet and jersey because Manning “didnt want to give up the real stuff.”

“The first we have since Eric saved it on his AOL account and the second we have since Eli apparently saved it on his AOL account,” Brook said.

“I do give Eli and his lawyers credit for not destroying evidence.”

Manning and John Mara attend an awards dinner on April 6.Charles Wenzelberg

The suit — set for trial Sept. 25 — initially was filed in 2014 by Inselberg, who in 2011 was among six memorabilia dealers charged by the feds in Chicago with selling fake game-used jerseys.

The other defendants all pleaded guilty, but Inselberg won dismissal of the indictment against him by arguing that witnesses — including Skiba and two other Giants employees — lied to the grand jury to cover up their own fake-memorabilia sales.

Inselberg’s co-plaintiffs include diehard Giants fan Michael Jakab, who shelled out $4,300 for a helmet purportedly worn by Manning during the team’s 2007 Super Bowl season — but which he claims is really just a “$4,000 paperweight.”

The final plaintiff is Sean Godown, a US Navy senior chief petty officer and Giants fan who sold the helmet to Jakab.

Court papers say Godown began collecting game-used memorabilia between tours of duty and bought the helmet for $5,000 on eBay, but decided to sell it at a loss “after he began to question its authenticity.”

In a statement, lawyers for the Giants said: “The email, taken out of context, was shared with the media by an unscrupulous memorabilia dealer and his counsel who for years has been seeking to leverage a big payday.”

“The email predates any litigation, and there was no legal obligation to store it on the Giants server,” the statement added.

“Eli Manning is well known for his integrity and this is just the latest misguided attempt to defame his character.”